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Drug-eluting Anodized Titanium Orthopedic Implants

C. Yao, T.J. WebsterBROWN University, US

Keywords:titanium, anodization

Abstract:It has been reported that the average functional lifetime of an orthopedic implant is 10 to 15 years. The inertness of titanium-based implants is a result of their spontaneously formed surface oxide layers. With the help of surface engineering, their cytocompatibility properties can be further improved. In this study, an electrochemical method known as anodization was used to modify the morphological and chemical properties of titanium surfaces (Fig. 1). The resulting titania nanotubular structures on titanium implant surfaces were about 60 nm wide (inner diameter) and 200 nm deep. In vitro studies found that anodized surfaces consisting of titania nanotube arrays were favored by bone-forming cells (osteoblasts) compared to unanodized surfaces. These titania nano-tubular structures were also utilized as novel drug delivery systems to inhibit infection and wound inflammation while increasing new bone formation. For this purpose, antibiotic drugs (penicillin and streptomycin) were loaded into these nanotubular structures by physical adsorption. To mediate interactions between drug molecules and nanotube walls, anodized titanium nanotubes were modified by silanization to possess amine or methyl groups on their surface instead of -OH groups (Fig.1). Results showed increased hydrophobicity of chemically modified titania nanotubes (methyl > amine > hydroxyl terminated surface). These drug loaded substrates were soaked in phosphate buffered solution in a simulated body environment to determine drug release behavior. Buffer solutions were collected and replaced every day. The eluted drug amounts were measured spectroscopically. Results showed more antibiotic penicillin and streptomycin release from chemically modified nanotubes compared to unanodized titanium substrates; specifically, titania anodized nanotubes functionalized with –OH groups performed the best (Fig. 2). In this manner, this study advances titanium currently used in orthopedics to possess drug release behavior which can improve orthopedic implant efficacy.